[U4R1A69]

I'm in the middle of selecting parts for a modified 428 rebuild. I'm new to Pontiac's and just read about cutting down your rod journals to fit BBC rods. I'm reusing the stock "N" crank. What are the pro's and con's of cutting down my stock crank and using 6.80 rods vice the 6.625?

[Steve Barcak]

There are some benefits on paper but, in the real world, probably not noticeable.

By offset grinding, you could pick up a few inches that way but, you would never feel it.

You could run chev size bearings, if you consider that advantage ( I do not ), it is auguable, esp in a street car.

If you run a 6.8 rod, you will need to buy custom pistons. If that is already in your budget, fine.

If you ran a 6.8 rod vs a 6.625", you would have a slightly better rod/stroke ratio too but, again, nothing you would notice in your street car.


Based on all that- unless you are already planning to buy a custom set of pistons and understand all the dimension changes you would need, it is not worth doing.

I would keep the stock Pontiac rod length and journal sizes. 428s are great motors the way the come, dimension wise, they are very well liked and respected too.

If someone made a .040" stroker kit including the custom pistons and offset ground crank already and at a good price, that would tip the scales the other direction and I would do it. Otherwise, I'd stay with stock journal/rod length dimensions.

Finally, understand that chev never made an engine with 6.8 bbc rods as your mentioned. That is an aftermarket dimension. Chev rods are much shorter than stock Pontiac rods, they are not longer. The 6.8" rod is an aftermarket rod for custom applications and not an actual chevy dimension. Do not feel bad not knowing- many others are also misleaded about that.

[steve25]

The lighter weight of the average 6.8" rod and the far lighter pistons and wrist pins over a stock deal will allow the motor to rev a good bunch faster, and in turn get the mass of the car moving faster also.
It also takes strain off of the main web area of the block so that even when employing higher rpms things are not as loaded as the stock parts would be at a lower rpm to some extent!

The smaller BB chevy rod bearing size allows less oil pressure to be needed and less heat put into the oil it self.
The need to cut the crank allows use of a a bigger radius to be cut on each side of the cranks rod jurnal. this makes for a stronger crank even though you have cut the rod jurnal to a smaller size.

If you are in need of buying new bottom end parts anyway, its a no brainer!

[Cliff R]

For a 428 street/strip engine, it's not worth the time, effort, or expense to cut down the 428 cranks for the longer rods.

Buy good rods and pistons in stock Pontiac dimensions. The biggest improvement in power comes from the lighter pistons/pins and modern ring pack, not from the longer rods and smaller journal diameter.....IMHO.....Cliff

[PONTIAC DUDE]

Originally Posted by Cliff R

For a 428 street/strip engine, it's not worth the time, effort, or expense to cut down the 428 cranks for the longer rods.

Buy good rods and pistons in stock Pontiac dimensions. The biggest improvement in power comes from the lighter pistons/pins and modern ring pack, not from the longer rods and smaller journal diameter.....IMHO.....Cliff

X 2, depending on the hp build or application.

[U4R1A69]

Thanks for all of the replies. I really appreciate all of the information.

[Buford T. JuSStice]

I would also keep in mind that going with longer rods you're going to need to consider the deck height (10.25" on Pontiac motors) vs how long the piston and rod assembly is going to be. If you use longer rods, you MUST use pistons that have shorter compression heights as well to make up for the extra reach, otherwise your pistons are going to hit the cylinder heads. This is what Steve Barack was referring to with custom pistons.

Consider the costs of machine work for the crank, and the block to accept the BBC rods, and the cost of the now necessary custom pistons, and everything else you're going to need to take into consideration that we haven't even mentioned here yet and then compare that to the benefits you would get out of it.

What exactly were your goals for your build? What did you want to do with it?

[U4R1A69]

The goals for this build is not to build it again and to have a daily driver of ~500Hp. I dont think the custom pistons is going to be an issue since Icon offers" Icon Forged Pistons 428 Long Rod 4.3 cc Valve Reliefs. For blocks using 4.0" stroke crank with BBC rod journals #IC-937" This is from PPR. These pistons are about the same price I'm going to pay regardless. The rods(Eagle) are offered pretty much everywhere for the same price I'm going to pay for standard rod . If reducing the journal size is going to possibly help save a rod bearing if I get a little crazy. Then the only factor I see is getting the crank cut down. The cost of getting my crank cut down is a extremely small price compared to this overall build. With this in mind it sounds like a cheap insurance.

[Buford T. JuSStice]

It's good to know there are other crazy fellas out there other than myself who want to make a daily driver out of a big displacement motor. I don't know if I would want to go with THAT much power, or have machine work done to the crank in my own build, but that's just me.

Do they offer replacement crankshafts that will work for your application? It may be wise to keep the original crank, rod and pistons together just in case... then again, if something goes wrong, there may be no second chance. There's nothing you can do about the size of your mains, and they will be put through much more stress with the kind of stroker set up you're doing. All you can do is make sure they're as close to clearance tolerances as possible, and make sure they're nice and secure with 4-bolt main bearing caps.

If I remember correctly, 428's came with 3.25" main bearings. If I were you, I would stick to keeping it a 428, and instead find a 400 to work with instead as it has the same bore as your 428, and the main journals are 3" instead. Essentially this will provide the same type of insurance for your main journals as what you're doing to your rods, as well as provide you with numerous other advantages. Finding a 4" stroke crankshaft with 3" mains is easy to do these days, so all you would need to do is buy the crank, and have it machined.

Just throwing in my pair of pennies.

[Ragtop Man]

Truth is the universal solvent, here.

Whether or not you actually need 500 hp is one thing if you need to to be competitive in a class or with a certain type of car; or do you want a car that feels like it has 500 hp, which is something completely different.

That HP level is a backwards layup with any decent aftermarket head and intake system and HR stick. But more important, keeping the strong low end grunt and brutal midrange of a Pontiac is where it's at.

Unless you are thrashing hell out of a drag motor, the bearing speed issue is a moot point; at most speeds on the street the speed is offset by the extra stiffness and surface area to support the rotating assembly. IIRC, the small-journal stroker industry popped out of the shrinkning pool of suitable large journal large displacement engines, not out of a theoretical discussion.

To me, the money play is to get a 455 crank, knock it out 30 over and work more on the combination; give it a little convertor and gear and you'll be telling your friends that you 'built too much motor for the car' .

[Mister Pontiac]

Originally Posted by Ragtop Man

Truth is the universal solvent, here.

Whether or not you actually need 500 hp is one thing if you need to to be competitive in a class or with a certain type of car; or do you want a car that feels like it has 500 hp, which is something completely different.

That HP level is a backwards layup with any decent aftermarket head and intake system and HR stick. But more important, keeping the strong low end grunt and brutal midrange of a Pontiac is where it's at.

Unless you are thrashing hell out of a drag motor, the bearing speed issue is a moot point; at most speeds on the street the speed is offset by the extra stiffness and surface area to support the rotating assembly. IIRC, the small-journal stroker industry popped out of the shrinkning pool of suitable large journal large displacement engines, not out of a theoretical discussion.

To me, the money play is to get a 455 crank, knock it out 30 over and work more on the combination; give it a little convertor and gear and you'll be telling your friends that you 'built too much motor for the car' .

Amen! X2...

[hurryinhoosier62]

X 3!!!